Conventionally, processing of utility and sewage water has often made use of a contact between gas and liquid in a container for the purposes of improving the efficiency of biological membrane processes by increasing the content of dissolved oxygen, and speeding up the decomposition of residual ozone. Similar processes have also been used for absorbing and removing various odorous substances from gas.
Typical methods for achieving such contact includes the method of pressurizing the interior of a vessel, and feeding air bubbles into the solution contained in the vessel with the aim of increasing the oxygen content in the solution. Pressurizing the interior of such a vessel can be achieved by using a jet flow or an ejector.
According to such methods, the air bubbles are broken into fine bubbles immediately after the pressurization and a favorable contact is established between the air and the liquid, but the bubbles have a tendency to grow into larger bubbles in time, and the increase in the oxygen content is often not sufficient for the specific purpose. It has also been conventionally practiced to fill the vessel with chamotte, anthracite and other natural minerals, inorganic foam materials, and molded synthetic resin materials, and pass the gas and the liquid through this vessel for the purpose of improving the contact between the gas and the liquid.
However, when natural minerals are used as a contact material, their particle diameters are so small and their gravitational weights so great that the gas would not be evenly distributed and mud balls tend to be generated, thus forming paths for liquid flow and reducing the efficiency of contact between the gas and the liquid. When natural foamed mineral material is used for the contact material, the particles of the contact material are too large, and the surfaces of contact material are prone to wear, which likewise has a detrimental effect on the efficiency of contact between the gas and the liquid.
When molded plastic pieces are used as the contact material, the turbulence of the flow is not so much as desired because the space between the particles is excessive and the particles have a uniform shape so that the efficiency of contact is not very high.
When odorous substances are desired to be removed from gas, according to a known process of contact between gas and liquid, the liquid is sprayed from an upper part of the vessel while the gas is introduced from a lower part of the vessel. In this case, metal mesh and Raschig ring are widely used as the contact materials. In either case, it is not possible to achieve a sufficiently high processing capability because the wire mesh simply restricts the gas flow without creating any substantial turbulence and the Raschig ring has an excessively large ratio of vacant space and has a highly uniform shape.